FIG. 1 is cutaway view of a related art reactor pressure vessel 100, such as an ESBWR pressure vessel. Vessel 100 includes a core plate 118 laterally supporting one or more fuel assemblies 110 within core shroud 114. Core shroud 114 separates upward flow of coolant through the core and assemblies 110 therein from downcomer annulus flow. Core plate 118 further supports core shroud 114 and may itself be supported by support ring and legs 102. Top guide 112 is positioned at a top of the core shroud 114 and potentially bolted to core shroud 114. Top guide 112 may be a grid structure that provides lateral support and positioning to the top of fuel assemblies 110. Each opening in top guide 112 can provide lateral support and guidance for four fuel assemblies 110 (or in the case of peripheral openings at the edge of the core, two or three fuel assemblies). One or more instrumentation tubes 150 and control rod drives 104 may extend through a bottom of vessel 100 for control and monitoring of the conditions in the core.
As liquid coolant boils among assemblies 110, a heated mixture of steam and water flows upward through top guide 112. Chimney 120 receives the energetic steam/water mixture exiting fuel assemblies 110. Partitions 121 in chimney 120 limit cross flow and minimize potential for recirculating eddies in this heated coolant moving up through reactor 100. Chimney 120 may be relatively long, such as over 28 feet in vertical length, to accommodate larger reactor designs and/or encourage longer inertial lengths for heated steam/water exiting a core of reactor 100.
Chimney 120 may be bolted to top guide 112 at a lower end and support steam separators 140 at an opposite end. Chimney head 122 may be bolted to chimney 120 and laterally supported by chimney restraint 123, which may be paired, slip-fitting brackets on chimney 120 and an inner wall of vessel 100. In this way, chimney 120 remains static in vessel 100 as the steam/water mixture rapidly flows up through chimney 120. After exiting chimney 120, the steam/water mixture is directed into steam separators 140 that include a flat base (or a small dome) with an array of standpipes thereon and a separator structure at the top of each standpipe. The separator structure and standpipes in steam separators 140 separate liquid water from the steam-water mixture rising therethrough. Steam from the steam separators 140 flows upward to steam dryers 141, where additional moisture is removed. The separated and removed liquid is directed into a downcomer annulus between the outer wall of chimney 120 and inner wall of vessel 100. The dried steam exiting steam dryers 141 is then directed into main steam lines 103 for electrical power production.
During a reactor outage, such as a refueling outage or other maintenance period, top head 105 of vessel 100 may be removed, and internal structures of vessel 100, such as steam dryers 141 and steam separators 140 may be removed to access the fuel assemblies 110. During such an outage, loading equipment may move and load new fuel assemblies 110 into reactor 100 while removing or shuffling older or spent fuel assemblies 110. Such moves may be made with top guide 112 and/or chimney 120 in place, if sufficient clearances are maintained in these structures.
FIG. 2 is a schematic of an example refueling floor 10 layout during a refueling outage, with reactor 100 shutdown and opened for refueling. As shown in FIG. 2, an equipment pool 15 and a buffer pool 20 may be available on refueling floor 10 for movement and storage of reactor components. An area 101 about reactor 100 may be filled with water, or flooded, above an open top of reactor 100, permitting liquid communication and submerged movement between pools 101, 15, and 20 on refueling floor 10, allowing submerged movement of components from reactor 100 and into/between pools 15 and 20. Pools 15 and 20 are typically about 22 feet deep when maximally flooded, as set by floor elevations on refueling floor 10. As seen in FIG. 2, steam dryer 141 may be removed from reactor 100 and placed in equipment pool 15 during an outage.